Decontamination of earthquake catalog from quarry blast events in northern Egypt

Abstract

Earthquake catalogs are often contaminated by man-made crustal activities such as quarry blasts. That is the case in northern Egypt, where many of cement quarries were working so long time ago since the beginning of the twentieth century (1911). Therefore, it is necessary and essential to separate these quarry blast events from the earthquakes for real seismicity and hazard analysis. Generally, discrimination of quarry blasts from tectonic events often done through different techniques and methods. In this study, the time and frequency-domain analyses of the Egyptian National Seismological Network (ENSN) digital seismograms have performed using three techniques and methods (S/P wave amplitude peak ratio, complexity, and spectral ratio). Moreover, the power of event (Pe) analysis comprising three techniques (S/P wave amplitude peak ratio, complexity, spectral ratio) was also used together to extend the discrimination accuracy as well. Finally, we have used a linear discrimination function (LDF) analysis. A total of 1473 seismic event waveforms (ML ≤ 3.0) from the ENSN digital database have been investigated. The obtained results indicate that for West of Nile Dislocation (zone no. 1) 78.1% of the investigated seismic events are tectonic events; however, 21.1% are quarry events and 0.8% are misclassified events. For the East Nile Dislocation (zone no. 2) 36.2% and 63.7% are earthquakes and quarry blast events, respectively and 0.1% are misclassified events. This means that the earthquake catalog for zone no. 2 in northern Egypt is highly contaminated and needs very high concern during the further treats especially with microearthquakes dataset for actually real seismicity and hazard analysis.